This invention relates to a workpiece transfer apparatus for transferring a workpiece, for example, from one of two adjacent pressing machines to the other.
A workpiece transfer apparatus of the type heretofore extensively used is disclosed, for example, in Japanese Laid-Open (Kokai) Utility Model Application No. 172627/86 and Japanese Utility Model Publication No. 55886/80. Such a conventional apparatus comprises a base, a first guide rail mounted on the base and extending vertically, a first slider mounted on the first guide rail for vertical movement, a second guide rail fixedly mounted on the first slider and extending horizontally, a second slider extending horizontally and movable horizontally along the second guide rail, and a plurality of suction devices mounted on the second slider. In this conventional apparatus, a table is provided between pressing machines. The vertical movement of the suction devices is effected by the vertical movement of the first slider, and the horizontal movement of the suction devices is effected by the horizontal movement of the second slider. One suction device moves horizontally toward one pressing machine from a basic position disposed between the pressing machines, and then descends to hold a workpiece, placed on a lower die of the one pressing machine, by suction, and then ascends, and then moves horizontally toward the table, and then descends to place the workpiece on the table. During this time, the other suction device holds another workpiece, placed on the table, by suction, and then places this workpiece on a lower die of the other pressing machine.
In the above workpiece transfer apparatus provided with the vertically movable slider and the horizontally movable slider, the workpiece remains unchanged in posture, that is, remains horizontal.
Recently, there have been required various pressing operations one example of which is to invert the workpiece removed from one pressing machine and then to press it. It is difficult for the above conventional apparatus to meet such requirement.
To meet such requirement, there has been proposed a workpiece transfer apparatus disclosed, for example, in Japanese Laid-Open Patent Application No. 81230/87. This apparatus comprises a vertically-extending guide rail mounted on a side surface of a pressing machine, a slider mounted on this guide rail for vertical movement, an arm angularly movably connected at one end to the slider, and a suction device angularly movably mounted on the other or distal end of the arm. The arm is angularly movable about a horizontal axis and also about a vertical axis. One thing to note here is that the apparatus is provided with only one arm, and that the transfer of the suction device is effected by the angular movement of this arm. The vertical movement of the suction device is effected by the vertical movement of the slider.
In the apparatus of the above Japanese Laid-Open Patent Application No. 81230/87, the transfer of the workpiece depends solely on the angular movement of the single arm mounted on the pressing machine via the slider, and therefore the distance of transfer can not be increased.
A workpiece transfer apparatus disclosed in Japanese Utility Model Publication No. 17593/84 comprises a base, a first arm mounted on the base for angular movement about a first angular movement axis, a second arm mounted at its upper end on an upper end of the first arm for angular movement about a second angular movement axis, and a suction device mounted on a lower end of the second arm for angular movement about a third angular movement axis. The first to third angular movement axes are disposed horizontally and are parallel to one another. The effective length of the first arm extending between the first and second angular movement axes is equal to the effective length of the second arm extending between the second and third angular movement axes. The suction device extends in a direction perpendicular to the third angular movement axis. This apparatus is provided with a single drive means. When the first arm is angularly moved through an angle .theta. by this drive means, for example, in a clockwise direction, the second arm is angularly moved relative to the first arm in a counterclockwise direction through an angle of 2.theta. via a power transmitting mechanism, so that the suction device is moved horizontally. At this time, the suction device is angularly moved relative to the second arm in a clockwise direction through an angle of .theta. via another power transmitting mechanism, and therefore the suction device is maintained in a horizontal condition.
In the workpiece transfer apparatus of the above Japanese Utility Model Publication No. 17593/84, there is not provided the function of vertically moving the suction device, and therefore it is almost impossible to hold and remove the workpiece by the suction device. The suction device extends in the direction perpendicular to the third angular movement axis, and therefore during the time when the suction device is inserted between upper and lower dies of one of the two pressing machines, the distal end of the second arm is also inserted between these upper and lower dies. Therefore, it is necessary to increase the distance between the two dies.